1. Field of the Invention
The invention relates to alloy wires and manufacturing methods thereof, and more specifically to alloy wires utilized for wire bonding of packages of electronic devices and manufacturing methods thereof.
2. Description of the Related Art
Wire bonding is an extremely important step in the packaging processes of semiconductor devices and light emitting diodes (LED). Bonding wires provide not only signal transmission and power transmission between chips and chip carriers (substrates), but also heat dissipation performance. Therefore, it is necessary for metal wires for wire bonding to have not only excellent electrical conductivity and thermal conductivity, but also sufficient strength and ductility. The hardness of the metal wires cannot be too high in order to prevent chips from cracking during hot pressing in the wire bonding step and have a good contact between the metal wires and the bond pads to have excellent bondability. Further, it is necessary for the metal wires to have well antioxidative activity and corrosion resistance because the polymer encapsulants for packaging commonly have corrosive chloride ions and hygroscopic property absorbing moisture from the environment. Moreover, the metal wire conducts a high volume of heat to the first bond (ball bond) when the ball bond cools from the molten state to room temperature, and thus, a heat affected zone is formed in the metal wire near the ball bond. Grain growth happens to the metal wire in the heat affected zone due to heat build-up, resulting in formation of local coarse grains. The local coarse grains provide a lower strength, and thus, the metal wire cracks in the heat affected zone during the wire pull test, negatively affecting the bonding strength. When completing the packaging processes of the semiconductor devices or the light emitting diodes, the high current density through the metal wires potentially activate atoms in the metal wires and thus generate electron migration during utilization of the packaged products. As a result, holes are formed at the terminal of the metal wires, resulting in a decrease in electrical conductivity and thermal conductivity, and even the occurrence of broken wires.
The bonding wires utilized in the present electronic industry are mainly pure gold and pure aluminum. Recently, pure copper wires (referring to US20060186544A1 and U.S. Pat. No. 4,986,856) and composite metal wires such as copper wires with gold plating (referring to U.S. Pat. No. 7,645,522B2), copper wires with palladium plating (referring to US 20030173659A1), copper wires with platinum plating (referring to US 20030173659A1) and aluminum wires with copper plating (referring to U.S. Pat. No. 6,178,623B1) are also being utilized for the bonding wires. The internal structures of the conventional metal wires for wire bonding are all equi-axial fine grains. The conventional fine grain structure may provide sufficient tensile strength and ductility. However, there are a lot of high angle grain boundaries existing between the fine grains. The high angle grain boundaries scatter the electron transmission, and thus increase the electrical resistivity of the metal wires and simultaneously decrease the thermal conductivity of the metal wires. On the other hand, the high angle grain boundaries have higher interfacial energy and provide favorable paths for environmental oxidation, sulfuration and chloride ion corrosion, lowering the reliability of packaged electronic products. Moreover, the heat affected zone tends to be formed in the metal wire with a fine grain structure near the first bond (ball bond) during wire bonding. Thus, the wire bonding strength is decreased, and electron migration tends to occur to the metal wire with a fine grain structure during utilization of packaged semiconductor devices or light emitting diodes, which are all main factors causing the deterioration of quality and reliability of conventional packaged products utilizing wire bonding technology.
Thus, alloy wires and manufacturing methods thereof are required to solve the described problems.